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Biomedical subjects

M Scheinman

Publications and source records attributed to M Scheinman.

At least 37 records · Page 2Linked to original sources
PubMed1994

Use-dependent properties of flecainide acetate in accessory atrioventricular pathways.

Flecainide acetate has been shown to have use-dependent properties. The use-dependent properties of flecainide were evaluated in 20 patients (13 men and 7 women, mean age 32 +/- 11 years) with accessory atrioventricular connections. Twenty to 30 stimulus drive trains were introduced in either the atrium or ventricle at progressively faster rates. The range of cycle lengths over which anterograde and retrograde conduction block occurred in the accessory pathway was assessed in the drug-free state and after oral loading with flecainide acetate. The block cycle length index was defined as the shortest cycle length during which 1:1 conduction was maintained in the accessory pathway minus the longest cycle length during which block in the accessory pathway occurred on the second paced beat. In the drug-free state, the (mean +/- SD) anterograde and retrograde block cycle length indexes were 20 +/- 12 and 20 +/- 9 ms, respectively. After flecainide therapy, the anterograde and retrograde block cycle length indexes increased to 80 +/- 33 and 65 +/- 29 ms, respectively (p = 0.002 compared with the drug-free state). The block cycle length index did not correlate with serum flecainide levels, but did correlate with other electrophysiologic markers of drug effect on accessory pathway conduction. The change in the block cycle length index demonstrates that flecainide has a progressive effect on accessory pathway conduction at more rapid rates, consistent with its in vitro use-dependent properties. This index is an excellent marker of drug efficacy.

Adult↗
PubMed1994

Supraventricular tachyarrhythmias: drug therapy versus catheter ablation.

Until recently, the only options available for treatment of supraventricular arrhythmias involved the use of drug therapy or cardiac surgery. However, over the past several years with the introduction of radiofrequency energy sources as well as steerable catheters, the clinician has a variety of additional nonpharmacologic options. This article reviews the use of pharmacologic therapy versus catheter ablation for the treatment of reentrant supraventricular arrhythmias, involving the atrioventricular junction and/or accessory atrioventricular connection, as well as arrhythmias emanating from the atria such as atrial fibrillation, atrial flutter, and atrial tachycardia.

Anti-Arrhythmia Agents↗
PubMed1993

Evaluation of edrophonium as a provocative agent for vasovagal syncope during head-up tilt-table testing.

Vasovagal syncope after head-up tilting is thought to be secondary to a complex, neurally-mediated reflex with both vasodepressor and cardioinhibitory efferent components. The efficacy of edrophonium, an acetylcholinesterase inhibitor, as a provocative agent for triggering syncope during head-up tilt testing was evaluated. Forty-five consecutive patients (22 female and 23 male) with history of recurrent unexplained syncope received edrophonium (10 mg intravenous) after 30 minutes of 60 degrees head-up tilting alone. Twenty normal control subjects (9 female and 11 male) were tested with head-up tilt testing and edrophonium. Syncope was induced in 19 of 45 patients with the diagnosis of unexplained syncope. In 9 patients who developed syncope with head-up tilting alone, the predominant hemodynamic finding was marked vasodepression. In contrast, in 10 patients who developed syncope only after head-up tilting and edrophonium, the predominant hemodynamic findings were marked vasodepression and bradycardia. Syncope was induced in 1 of 20 normal subjects after head-up tilting and edrophonium. There was no long-term complication from using edrophonium. It is concluded that head-up tilt testing with edrophonium: (1) significantly increases the identification of patients with vasovagal syncope, (2) may be particularly useful when provocation with isoproterenol is undesirable, and (3) may be an effective method to help differentiate patients with a significant reflex cardioinhibitory component from those with a predominantly reflex vasodepressor component.

Adolescent↗
PubMed1993

Evaluation and management of patients with polymorphic ventricular tachycardia.

This article reviews the current understanding of the mechanisms for polymorphic VT, its clinical manifestation, and therapies. The various idiopathic long QT syndromes and acquired forms of this entity are addressed, and a new syndrome of polymorphic VT associated with a normal heart and normal QT interval is emphasized.

Humans↗
PubMed1992

Stimulation of the summit of the right ventricular aspect of the ventricular septum during orthodromic atrioventricular reentrant tachycardia.

Application of ventricular premature complexes (VPCs) from the right ventricular (RV) apex during orthodromic atrioventricular (AV) reentrant tachycardia has limitations both in the ability to shorten the succeeding atrial cycle length and in helping to identify accessory pathway location. Stimulation from the summit of the RV aspect of the septum during AV reentrant tachycardia was investigated as a new technique to improve the diagnostic utility of applying VPCs during AV reentrant tachycardia. VPCs were induced during AV reentrant tachycardia at 10 ms decrements in patients with left free wall (n = 15), posteroseptal (n = 5), and right free wall (n = 3) accessory pathways from the RV apex and then from the summit of the RV septum. When the His was refractory, shortening of the atrial cycle length was noted in 13% of patients with left free wall pathways, in 60% of patients with posteroseptal pathways, and in 100% of patients with right free wall pathways with VPCs from the RV apex, and in 47, 100 and 100%, respectively, with VPCs from the summit of the septum. When all VPCs were considered, there was a significant shortening of the atrial cycle length in 67% of patients with left free wall pathways when stimulated from the RV apex, which increased to 93% with summit stimulation. An extrastimulus applied on or after the His effected a significant shortening of the atrial cycle length in no patients with left free wall pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Histologic findings of the heart and the conduction system in the first patient who underwent catheter ablation.

This is a detailed pathological examination of the heart including the conduction system (CS) from a 64-year-old male who had catheter ablation of the atrioventricular (AV) junction for intractable atrial fibrillation. This is the world's first human who had this procedure, and who survived 3 years and 8 months, and later died of congestive heart failure. Pathologically, the heart was hypertrophied and enlarged. Histologically, there were chronic inflammatory cells, marked fatty metamorphosis with fibrosis of the atria, the approaches to the AV node, and the AV node, with almost isolation of the node from the atria, and considerable fibrosis of the bundle and bundle branches. In addition, there was fibrosis of the summit of the ventricular septum with chronic inflammatory cells. These represent the sequelae of the ablation procedures. It is not known how much of the pathological findings contributed to the cardiac hypertrophy and impairment of cardiac function.

Atrial Fibrillation↗
PubMed1991

Percutaneous radiofrequency catheter ablation for supraventricular arrhythmias in children.

Nineteen procedures were performed in 17 children, aged 10 months to 17 years, using catheter radiofrequency applications for the management of malignant or drug-resistant supraventricular tachyarrhythmias. Diagnoses were junctional ectopic tachycardia in 1 patient, atrioventricular (AV) node reentrant tachycardia in 4 and accessory pathway-mediated tachycardia in 12. Accessory pathway locations were left lateral (n = 4), posteroseptal (n = 3), left posterior (n = 2), right posterolateral (n = 1), right posterior paraseptal (n = 1), right intermediate septal (n = 1) and right anterior (n = 1). Ablation of accessory pathways was performed using 20 to 40 W of energy. The catheter was passed retrograde to the left ventricle in patients with a left-sided pathway and anterograde to the right atrium in those with a right-sided or posteroseptal pathway. In the 12 patients with an accessory pathway, radiofrequency applications were successful in 11 pathways and failed in 2. There were no recurrences of accessory pathway-mediated tachycardia. Atrioventricular node reentrant tachycardia was treated by AV node modification using 15 W of energy applied until first degree AV block occurred. After radiofrequency catheter ablation, there was a prolonged AH interval, tachycardia was not inducible and tachycardia recurred in one patient. For the patient with junctional ectopic tachycardia, 15 to 18 W of energy was delivered at the site of the maximal His bundle electrogram until sinus rhythm and normal AV conduction appeared. After a recurrence, a second procedure abolished tachycardia and AV conduction. In summary, radiofrequency catheter ablation was initially successful in 17 of 19 procedures and ultimately curative in 14 (82%) of 17 patients with no serious complications. Radiofrequency catheter ablation appears to be a safe and effective method for the management of supraventricular tachyarrhythmias in children.

Adolescent↗
PubMed1991

Junctional tachycardias: anatomic substrate and its significance in ablative procedures.

The conduction system was studied by serial section in three patients with intractable supraventricular tachycardias originating from the atrioventricular (AV) junction who died suddenly. The three patients were a 6 month old girl (Case 1), a 5 month old boy (Case 2) and a 22 year old woman (Case 3). The latter had a pacemaker inserted after surgical ablation of the AV node. The heart was hypertrophied and enlarged in all. In Case 1, the AV node was partly within the central fibrous body and there was a left-sided AV bundle with acute necrosis in the summit of the ventricular septum, adjacent to the AV node and bundle. In Case 2, the coronary sinus was displaced cranially close to the central fibrous body, resulting in abnormality of the latter, with entrapment, distortion and division of the AV node and bundle into two distinct components within the central fibrous body. In Case 3, a left-sided AV node was connected to the atrial septum. The right AV node was completely interrupted by sutures and the penetrating and branching bundle and bundle branches were markedly fibrosed. In addition, the atrial septum and summit of the ventricular septum showed marked inflammatory reaction with fibrosis, which was more marked on the right ventricular side. Histologic examination of the conduction system in all three cases demonstrated congenital abnormalities of the AV junction that may be related to the tachycardia. These findings emphasize the need to carefully evaluate the atrial septum and AV junctional area, including the coronary sinus, before ablative procedures are undertaken.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Catheter ablation of the atrioventricular junction using a helical microwave antenna: a novel means of coupling energy to the endocardium.

Catheter ablation with either direct current defibrillator discharges or radiofrequency energy produces tissue injury via current flow from an electrode into the adjacent myocardium. In order to affect tissue at a distance, excessive power density may be produced at the electrode-tissue interface with the possibility of explosive gas formation or coagulum formation. A novel microwave catheter was developed with a helical antenna distally. This coil, although not in direct contact with the endocardium, radiates an electromagnetic field into the tissue that, in turn, causes thermal injury. The utility of this system for ablation was assessed in six dogs. The antenna catheter was introduced percutaneously and positioned so as to record the largest His electrogram. Microwave power (50 watts at 2,450 MHz) was applied for 114 +/- 118 seconds. Complete AV block was produced in all six animals with 1.8 +/- 1.2 applications. There was no ventricular ectopy or change in blood pressure during microwave ablation. One dog died 6 days after ablation. The remaining five dogs had persistent, complete AV block during 6 weeks of follow-up. Pathological analysis at 6 weeks revealed a large (mean 2.8 x 4.7 mm) fibrovascular scar in the region of the AV junction. Percutaneous microwave ablation of the endocardium appears feasible. By radiating an electromagnetic field without direct contact, this system can produce large lesions without being limited by desiccation of tissue and impedance rise.

Animals↗
PubMed1991

Polymorphous ventricular tachycardia associated with acute myocardial infarction.

BACKGROUND: During a 2.9-year period, 11 patients developed polymorphous ventricular tachycardia 1-13 days after acute anterior (seven patients) or inferior (four patients) myocardial infarction. None of the 11 patients had sinus bradycardia (mean heart rate, 90 +/- 23 beats/min), but three had a sinus pause immediately before the onset of polymorphous ventricular tachycardia. In all 11 patients, the QT interval and corrected QT interval (QTc) were normal or minimally prolonged (QT, 385 +/- 34 msec; QTc, 442 +/- 40 msec). None had significant hypokalemia (mean serum potassium concentration, 4.3 +/- 0.5 meq/l) or a grossly abnormal serum magnesium or calcium concentration (2.1 +/- 0.4 and 8.9 +/- 0.7 mg/dl, respectively). METHODS AND RESULTS: Immediately before the onset of polymorphous ventricular tachycardia, symptoms and/or electrocardiographic changes consistent with recurrent myocardial ischemia occurred in nine of 11 patients. One patient died before drug therapy could be initiated. Lidocaine was used in 10 patients and proved to be effective in only one. Intravenous procainamide was used in six patients: one improved, and five had recurrence of polymorphous ventricular tachycardia. Bretylium was used in five patients and was ineffective in all cases. Overdrive pacing was used in four patients and failed to suppress recurrent arrhythmias in all cases. Four patients with persistent polymorphous ventricular tachycardia unresponsive to lidocaine, procainamide, or bretylium responded to intravenous amiodarone. One patient with polymorphous ventricular tachycardia that was consistently preceded by ST segment elevation responded to intravenous nitroglycerin. Two patients with persistent polymorphous ventricular tachycardia and obvious recurrent ischemia unresponsive to pharmacological intervention responded to emergency coronary revascularization. A third patient who experienced recurrent angina and polymorphous tachycardia was initially stabilized with pharmacological therapy but subsequently underwent elective revascularization and has remained stable without antiarrhythmic therapy. CONCLUSIONS: Post-myocardial infarction polymorphous ventricular tachycardia is not consistently related to an abnormally long QT interval, sinus bradycardia, preceding sinus pauses, or electrolyte abnormalities. This arrhythmia has a variable response to class I antiarrhythmics but may be suppressed by intravenous amiodarone therapy. It is often associated with signs or symptoms of recurrent myocardial ischemia. Furthermore, coronary revascularization appears to be effective in preventing the recurrence of polymorphous ventricular tachycardia when associated with recurrent postinfarction angina.

Aged↗
PubMed1990

Catheter and surgical treatment of cardiac arrhythmias.

Over the past decade, numerous impressive advances have been made using nonpharmacologic methods for control of cardiac arrhythmias. These methods include surgical or catheter ablation of abnormal foci. Current techniques involve catheter ablation of the atrioventricular junction to control supraventricular arrhythmias. In addition, surgical techniques have proved to be remarkably safe and effective for treatment of patients with accessory pathways and those with atrioventricular nodal reentrant tachycardia. Patients with drug-refractory ventricular tachycardia may benefit from surgical resection of the ventricular tachycardia focus. The use of these interventional methodologies has radically altered the approach to management of patients with drug-refractory cardiac arrhythmias.

Electrocoagulation↗
PubMed1989

ECG left anterior fascicular block reveals diverse patterns on scintigraphic phase analysis.

Left anterior fascicular block (LAFB) remains an uncertain diagnosis by scalar ECG, particularly with coexisting inferior infarction. To assess the use of phase analysis in LAFB, left ventricular phase and amplitude maps were evaluated in the 70-degree left anterior oblique projection in eight control patients and 13 patients with LAFB who met the ECG criteria of Warner et al. The left ventricular region was divided into anterior (A) and inferior (I) segments. Contraction patterns were assessed by examination of the sequence of phase angles (phi), relative contraction time of the anterior versus inferior segments was assessed from the difference between segment mean phase angles, delta phi A-I, determined from the phase histogram, and duration of contraction was assessed by histogram width. Relative stroke volume was assessed on the amplitude image. Eight control subjects had normal amplitude, contraction of the anterior before inferior segment, narrow histogram width, and a normal ECG. Among the 13 patients with ECG LAFB, seven were concordant, with phase analysis demonstrating anterior contraction delay. Two of seven patients had narrow histograms and normal amplitude, which were compatible with isolated anterior conduction delay, and five of seven patients had broad histograms and reduced anterior amplitude, compatible with anterior infarction. Phase analysis was discordant with ECG LAFB diagnosis in six patients. All showed contraction of anterior segments before inferior segments as in normal subjects. Four had broad histograms and reduced inferior amplitude, compatible with prior inferior infarction without LAFB, and two had normal phase and amplitude maps. Phase patterns appear characteristic of LAFB with or without associated infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Bundle-Branch Block↗
PubMed1988

Gallium lung scintigraphy in amiodarone pulmonary toxicity.

We sought to assess the role of gallium-67 lung scintigrams in the evaluation of amiodarone pulmonary toxicity. Images and laboratory studies were evaluated in 54 patients who had chest radiographs and scintigraphic studies during amiodarone treatment of more than one month's duration among 561 patients receiving the medication for refractory arrhythmias. There were 22 patients with pulmonary symptoms and clinical evidence of amiodarone pulmonary toxicity (group 1); 19 patients had other causes for pulmonary symptoms (group 2); and 21 patients were without symptoms or other clinical evidence of pulmonary toxicity (group 3). There was no difference among groups in treatment duration or total amiodarone dose. Symptomatic presentation could not differentiate between group 1 and group 2 patients. However, radiographic findings of isolated pulmonary congestion or a normal radiograph in the presence of symptoms made amiodarone toxicity unlikely, while the appearance of new, dense radiographic infiltrates--often in a nodular distribution--were more frequent among group 1 patients (p less than 0.01). During symptomatic periods, 18 of 22 group 1 patients had abnormal gallium lung uptake, while four revealed more subtle serial changes but there was only one abnormal scintigram among symptomatic group 2 patients. Nonspecific radiographic abnormalities in patients with pulmonary symptoms on amiodarone therapy were rarely attributed to toxicity in the presence of a normal scintigram. One group 3 patient developed scintigraphic abnormalities early during amiodarone treatment, suggesting toxicity in the presence of a normal chest x-ray examination. Comparison of radiographic and scintigraphic studies performed during symptoms with those performed prior to symptom development best indicated the diagnosis, while comparison with later images assessed the efficacy of treatment. Diffusion capacity testing and transbronchial biopsy were sensitive but not specific for the diagnosis of amiodarone toxicity. Gallium image abnormalities parallel the development of amiodarone pulmonary toxicity and aid this diagnosis, especially when the chest radiograph is abnormal and ambiguous. Serial increments in scintigraphic abnormality appear especially helpful for diagnosis in the population at risk.

Adult↗
PubMed1987

Augmented preexcitation assessed by scintigraphic phase analysis during atrial pacing.

We sought to characterize the effect of augmented preexcitation on the phase image pattern associated with scintigraphic acquisition during conduction via accessory arteriovenous connections. For this reason we assessed phase image scintigraphy, acquired in sinus rhythm and during rapid atrial pacing in 12 patients with documented right (five patients) or left (seven patients) lateral accessory pathways. Augmented preexcitation during atrial pacing was documented at electrophysiologic study in all patients during atrial pacing at similar rates. Phase analysis was abnormal in only 8 patients during sinus rhythm but in all 12 patients during atrial pacing. Atrial pacing brought a significant delay in both mean left and right ventricular phase angles, LV phi and RV phi, respectively. With atrial pacing, the site of earliest phase angle, interpreted to indicate the site of earliest excitation, shifted to the site of the accessory pathway. There was increased relative "prematurity" of the mean phase angle of the ipsilateral ventricle and an absolute increase in the difference between mean and earliest left and right ventricular phase angles, delta phi (LV-RV) and delta phi 0 (LV-RV), respectively. In patients with right-sided pathways, delta phi (LV-RV) increased from 9.5 +/- 12.6 degrees to 47.9 +/- 22.8 degrees, whereas delta phi 0 (LV-RV) increased from 28.1 +/- 18.0 degrees to 67.6 +/- 25.0 degrees (both p less than 0.05). Patients with left-sided pathways demonstrated similar changes in which delta phi (LV-RV) decreased from 2.9 +/- 10.8 degrees to -26.5 +/- 9.0 degrees and delta phi 0 (LV-RV) decreased from 3.4 +/- 14.2 degrees to -27.4 +/- 17.9 degrees (both p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Hemodynamic and electrophysiologic effects of encainide in patients with bundle branch block.

Electrophysiologic studies were performed in 6 consecutive patients with bundle branch block and organic heart disease. All were studied after intravenous (0.9 mg/kg) encainide and 3 of the 6 after 36-72 hours of oral encainide (50 mg every 6 hours). After intravenous encainide, mean H-Q increased from 51 +/- 20 msec to 58 +/- 25 msec (14% p less than or equal to .05). After oral encainide (3 patients) H-Q increased to 90 +/- 39 msec (56% p less than or equal to .05, compared to baseline). Programmed ventricular stimulation was performed in 5. In 1 patient without spontaneous ventricular tachycardia, tachycardia was non-inducible before and after encainide. Of 5 patients with spontaneous arrhythmia, 3 had ventricular tachycardia induced before and after intravenous encainide at mean cycle lengths of 287 +/- 130 msec and 407 +/- 261 msec, (not significant) respectively, while 1 had ventricular tachycardia induced only after encainide. Four patients began chronic treatment with oral encainide (2 patients with inducible rapid ventricular tachycardia after encainide were excluded). All suffered major adverse outcomes. One died suddenly after an electrophysiology study demonstrated inducible ventricular tachycardia, which occurred only after encainide. One experienced new syncope after baseline H-Q increased 75% after encainide. Two patients developed new sustained atrial tachycardias and 1 patient developed persistent ventricular tachycardia on encainide.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗